Universal-Serial-Bus (USB) has been widely deployed as a standard bus for connecting peripherals such as digital cameras and music players to personal computers (PCs) and other devices. To facilitate discussion, FIG. 1A shows a prior-art peripheral-side USB connector. USB connector 10 is a male connector, also known as a USB plug. In the example of FIG. 1A, USB connector 10 represents a type-A USB connector. In use, USB connector 10 may be mounted on a board in the peripheral, or may be connected to the peripheral using a cable having a set of conductors. USB connector 10 can also be mounted in an opening in a plastic case (not shown) for the peripheral.
USB connector 10 contains a small connector substrate 14, which may be formed of white ceramic, black rigid plastic, or another sturdy substrate. Connector substrate 14 has four or more metal contacts 16 formed thereon. Metal contacts 16 carry the USB signals generated or received by a controller chip in the peripheral. USB signals typically include power, ground, and serial differential data D+, D−.
USB connector 10 contains a metal case that wraps around connector substrate 14. The metal case touches connector substrate 14 on three of the sides of connector substrate 14. The top side of connector substrate 14, holding metal contacts 16, has a large gap between itself and the top of the metal case. On the top and bottom of this metal case are formed holes 12.
FIG. 1B shows a host-side USB connector, also known as a female USB connector or a USB socket (receptacle). Female USB connector 20 can be an integral part of a host or PC, or can be connected by a cable. Another connector substrate 22 contains four metal contacts 24 that make electrical contact with the four metal contacts 16 of the male USB connector 10 of FIG. 1A. Connector substrate 22 is wrapped by a metal case, but three small gaps are formed between the metal case and connector substrate 22 around three sides of connector substrate 22. In FIG. 1B, these three gaps are seen on the left, right, and bottom sides of connector substrate 22 of FIG. 1B. A larger gap exists between the top of connector substrate 22 and the metal case as seen.
When male USB connector 10 of FIG. 1A is flipped over and inserted into female USB connector 20 of FIG. 1B, metal springs 18 of female USB connector 20 lock into holes 12 of male USB connector 10. This allows the metal casings to be connected together and grounded.
Currently, USB has a transfer rate of around 480 Mb/s, which is sufficient for some but not all applications. As a consequence, faster serial-bus interfaces are being introduced to address different requirements. PCI Express, at 2.5 Gb/s, and SATA, at 1.5 Gb/s and 3.0 Gb/s, are two examples of high-speed serial bus interfaces for the next generation devices, as are IEEE 1394 and Serial Attached Small-Computer System Interface (SCSI). PCI Express is an extension of the Peripheral Component Interconnect (PCI) bus protocol, which is a well-known protocol for interconnection components in a computer system. SATA stands for serial advanced technology attachment (SATA), which is an extension of the well-known AT attachment protocol employed to attach hard disks to computer systems. IEEE 1394 and SCSI are alternative bus protocols supporting high speed transfers.
Physically speaking, these other protocols (e.g., PCI-Express, SATA, IEEE 1394, SCSI, etc.) employ different form factors for their plugs and connectors. To facilitate discussion, FIGS. 2 and 3 show an ExpressCard and its connector. ExpressCard is a new removable-card form-factor that has been developed by the Personal-Computer Memory Card International Association (PCMCIA), PCI, and USB standards groups. ExpressCard 26 of FIG. 2 is about 75 mm long, 34 mm wide, and 5 mm thick and has ExpressCard connector 28.
FIG. 3 shows that ExpressCard connector 28 fits into connector or socket 30 on a host when ExpressCard 26 is inserted into an ExpressCard slot on the host. Since ExpressCard connector 28 and socket 30 are 26-pin connectors, they contain a greater number of signal pins than a 4-pin USB connector and are physically larger as well.
From an electrical standpoint, the higher data transfer rates of the non-USB protocols discussed above are highly desirable for certain applications. For example, PCI Express supports data rates up to 2.5 G/b, which is much higher than the data rate for USB. As another example, the serial AT-attachment (SATA) protocol supports data rates of 1.5 Gb/s and 3.0 Gb/s, which are also higher than the data rate for USB.
However, these non-USB protocols require a greater number of contact pins between their male connectors and female sockets, which in turn necessitates the use of relatively large connectors. For example, while the ExpressCard standard is useful for its higher possible data rates, the 26-pin connectors and wider card-like form factor limit the use of ExpressCards. As another example, SATA uses two connectors, one 7-pin connector for signals and another 15-pin connector for power. Due to its clumsiness, SATA is more useful for internal storage expansion than for external peripherals.
Accordingly, the choice up to now has been between the smaller form-factor but slower USB protocol/connectors and the bulkier but faster non-USB protocol/connectors. Neither choice is desirable to implement modern high-speed, miniaturized electronic devices and peripherals.